Oracle - Sorting Alphanumeric values with REGEXP_INSTR

SELECT PRODNAME, CAST(SUBSTR(PRODNAME,REGEXP_INSTR(PRODNAME,'[0-9]'),

LENGTH(PRODNAME) - (REGEXP_INSTR(PRODNAME,'[0-9]') - 1)) AS NUMBER)
AS EXTRACTDIGIT
FROM TEMPALPHANUMERIC
ORDER BY EXTRACTDIGIT